This disclosure is directed to a controller to be used with various types of gas lift wells including a piston lift producing well. The controller works well with a well which produces oil or gas or both. The typical well incorporates a casing and a tubing string in the casing. In one mode of production, a piston in the tubing string is permitted to travel from bottom to top lifting a slug of oil above the piston. It is lifted by injecting gas below the piston. The piston, therefore, functions as a pump piston on the upstroke. When the piston reaches the top, it is permitted to fall back to the bottom to gather another slug of oil. This procedure ordinarily requires the injection of surface gas into the casing, or perhaps into a string of macaroni pipe adjacent to the production tubing string. Alternate gas lift production techniques include gas lift wells, both continuous and intermittent with or without gas lift valves.
This controller responds to a number of well conditions detected by sensors. The well conditions include arrival of the piston at the top end. Other conditions also include casing pressure and production tubing pressure. These pressure levels are indicative of the operative condition of the well and in particular whether or not it is ready to deliver a slug of oil. In other production procedures, the well head sensors respond to conditions to signal the device of this disclosure. This invention is a controller typically installed on a well at a remote location where electrical power is not readily available. The device is normally installed in a housing at the well head. This environment is normally dangerous because natural gas may escape in the near vicinity. The device of this disclosure utilizes relatively low voltage batteries so that the device is intrinsically safe in that kind of atmosphere. The safety of this device is indicated by the fact that the device does not form sparks which might ignite natural gas in the near vicinity.
There are several problems relating to the use of this device, and the novel and unobvious controller of this disclosure has overcome these problems. One problem that has been overcome and, hence, one advantage of this apparatus is the use of a battery supply coupled with a battery voltage monitor. This monitor forms a signal indicated on a visible display alerting service personnel to the fact that batteries need replacing. Preferably, the device is set at a very high level so that only a slight drop in terminal voltage triggers the alarm in operation. While there might be many more weeks or months of life in the batteries, field service personnel happening by will observe the signal and replace the batteries prior to failure. This early warning system prevents the well from being poorly operated as a result of battery failure.
Another problem overcome by this apparatus and, hence, another feature of this disclosure is the use of a CMOS 8 bit microcomputer which is operated with a duty cycle of far less than 1%. The device is, for all intents and purposes, switched off. It is equipped with a non-volatile memory. The microcomputer and its associated memory are thus in an off state most of the time and require nil power to maintain this condition. The device is switched on occasionally by a timing circuit which causes it to cycle on at which time the variables from the sensors are tested to determine the operative state of the well. If it is determined that the equipment should be switched to thereby change a valve and alter operation of the well, a pilot valve for the main control valve is operated by pulsed solenoids. The pilot valve does not require the continued application of power; rather, it is switched on only by pulses. When it is on, it operates for only an interval. This interval is in the millisecond range but it is sufficient to change the operative state of the pilot valve.
This device, thus, comprises a relatively small apparatus typically fitting within an enclosure of about 200 cubic inches or less. This enclosure houses a battery pack, the controller of this disclosure and the output pilot valve. It is nicely reduced in size to enable full enclosure within a single housing for safety sake. Moreover, it operates at low voltages and, therefore, is intrinsically safe from explosion. The device further utilizes a battery pack for remote field installations. It further features non-volatile memory and CMOS microcomputer components which enable the components to be switched off in a duty cycle which is far less than 1%.
Many other features and objects of this structure will be observed upon a review of the detailed disclosure which is included below.